Method of making foundry moulds and cores

ABSTRACT

A process of producing foundry moulds and cores from a moulding sand or sand mixture, containing moulding sand, hydraulic cement as a binder, an alkali-metal aluminate, an alkali-metal carbonate and a surface-active material.

106-89. AU 115 EX United States Patent 1 1 1111 3,874,885

Lyass et a1. 1 Apr. 1, 1975 METHOD OF MAKING FOUNDRY MOULDS 106/89, 97;164/23 AND CORES [76] Inventors: Abram Moiseevich Lyass, [56] ReferencesCited Sharikopodshipnikovskaya ulitsa, 2, UNITED STATES PATENTS ha 146;Pavel Afanasievich Borsuk,

Nizhne pervomaiskaya umsay 59, 1,748,839 2/1930 Grunewald 106/972,806,530 9/1957 Binkle 106/89 10; Zkhmb 6.3mm Ogly 2880.096 3/1959Hurley 106/97 Usubov, cherkllovskayfl uhlsa 3,140,956 7/1964 Kamlet eta1 .0 106/97 kvarml 8-11, kofiws 106; 3,196,505 7/1965 Moren 106/38.9Vikt0r Georgievich Kuzentsov. 5 3,600,203 8/1971 Turin 106/383Kozhukhovskaya ulitsa, 10, kv. 36, 3,666,703 5/1972 Murata ct a1.260/294 2111 of Moscow, U.S.S.R.

[22] Filed: 28, 1972 Primary Evaminer-Lorenzo B. Hayes Attorney, Agent.or Firm-Holman & Stern [21] Appl. N0.: 248,380

[57] ABSTRACT A process of producing foundry moulds and cores 7 from amoulding sand or sand mixture, containing mouldin sggd, 11y d r;1 11 icqg1 1ent as a binder, an al- [52] 1. .5. Cl 106/38.35, 106/38.9,1066/879, T m an H ahmeml Carbonate anda H 1 Int Cl g surface-fictivematerial.

Field Of Search l06/38.3, 38.35 38.9, claims, 1 Drawing Figure [30]Foreign Application Priority Data Feb. 11 1971 U.S.S.R 1615586 HOURSMETHOD OF MAKING FOUNDRY MOULDS AND CORES BACKGROUND OF THE INVENTIONThe present invention relates to foundry work and more particularly to aprocess of making foundry moulds and cores from a fluid self-hardeningmoulding sand or sand mixture.

By using the above mixtures such operations as the compacting of themoulding sand and drying of the moulds and cores produced thereof can beavoided, dimensional accuracy of castings and efficiency of the processare enhanced.

Well known are the processes of manufacturing foundry moulds and coresbased on the use of fluid selfhardening sand mixtures containing a smallamount of a surface-active material which ensures the conversion of themixture to a fluid state.

One of these sand mixtures contains a moulding sand, an alkali-metalsilicate as a binding agent, dicalcium silicate as a hardener and asurface-active material (see, for example, French Pat. No. 1,342,529).

The above sand mixture proved successful, though the hardening rate andstrength control is rather difficult to predict because thedicalcium-silicatecontaining material is a waste product varying indicalcium silicate content and, hence, perties are unique to this sandmixture. Moreover, the knockout of the cores made from the above sandmixtures presents a serious problem.

Attempts also have been made to provide a fluid selfhardening sandmixture containing cement as a binder (see, for instance, English Pat.No. 1,085,65l, French Additional Pat. No. 87,456).

The sand mixture features stable properties, though typical of themoulds and cores manufactured of the above mixture is a low hardeningrate and inadequate strength. The compression strength of the sandmixture within l hr after manufacture does not exceed, as a rule, 1kg/cm which precludes the possibility of using the mixture for theproduction of heavy cores of intricate shape.

It is an object of the present invention to overcome or at least todiminish the above difficulties.

SUMMARY OF THE INVENTION The present invention has the principal objectto provide a process of making foundry moulds and cores from a fluidself-hardening sand or sand mixture with controllable properties, suchas: hardening rate and strength.

This is achieved by the fact that in a sand mixture containing mouldingsand, hydraulic cement as a binder and a surface-active material,according to the invention, an alkali-metal aluminate and an alkalimetalcarbonate are introduced during production.

The alkali-metal aluminate enables more rapid hardening of the fluidsand mixture.

Most advantageous is the addition of the alkali-metal aluminate in anamount ranging between 0.25] .5 percent of the weight of the mouldingsand. Usually sodium aluminate is employed being among the compoundsmost widespread in the industry. According to the present invention,sodium aluminate is introduced into the fluid sand mixture in a liquidstate. It would be expedient to employ sodium aluminate of a specificgravity of 1.48-1.68 g/cm with a molar ratio of N320: A1 0 of betweenMal and 1.521. Sodium aluminate is an active hardening accelerator,therefore its addition even in small amounts substantially reduces theflowability of the sand. As the contents of sodium aluminate in thefluid sand mixture increases, a moment might occur when the mixturecompletely loses its flowability by hardening during the preparationcycle.

According to the present invention an alkali-metal carbonate is alsoadded to the fluid sand mixture. Most effective is potassium carbonate.

Potassium carbonate assists in increasing the bench life of the sandmixture, decelerates the sand hardening at the initial stage andenhances its strength at the late hardening stage. Fluidizing capacityof potassium carbonate offers a two-fold reduction in the amount offoaming agent, preserving meanwhile high flowability of the sand mixturewhich enhances its strength. Preferably, the content of the alkali-metalcarbonate in the sand mixture shall amount to 0.5-2 percent of theweight of the moulding sand.

According to a preferred embodiment of the present invention a fluidself-hardening sand might contain parts by weight of moulding sand, forexample, quartz, 10 parts by weight of Portland cement, 6 parts byweight of water, 0.1 part by weight of a surface-active material. Theamounts of sodium aluminate and potassium carbonate are given in Tablel. The sand and Portland cement are mixed for 1-2 min. Then a liquidcomposition is prepared by dissolving potassium carbonate in water andadding the surface-active material and sodium aluminate to the solution.Next the liquid composition produced thereby is introduced into thesand-Portland cement mixture and stirred until the mixture is convertedto a fluid state.

In the accompanying graph the x-axis indicates the hardening time orholding time of the foundry moulds and cores in air in hours and they-axis shows compression strength in kglcm Variation of compressionstrengths of the foundry moulds and cores manufactured of sand mixturesof l, 2 and 3 of Table 1 respectively with their air hardening time isillustrated by curves A, B and C.

As shown by the graph and Table I, the higher the potassium carbonatecontent of a sand mixture, the greater amount of sodium aluminate can beintroduced into the mixture and the higher will be the hardening rate ofthe sand mixture (curve C).

According to the present invention the binder is cement, such asPortland cement, alumina cement, their mixtures or neat cements.

Conforming to this invention, a specific surface area of a cement exertsan appreciable influence upon the hardening rate of a fluid sandmixture. The larger the specific surface area of cement, the higher thehardening rate and strength which can be attained for a given fluid sandmixture. By changing the specific surface area of cement it is possibleto control the mixture hardening rate. The properties of sand mixture 1,containing Portland cement with a different specific sur- Table 1 Partsby weight ground material and calculated by the Causenie- Carmandmethod.

For the objects specified in the present invention several types ofsurface-active materials can be advantageously used, such as: anion,cation, nonionogenic materials and/or a mixture of these. Such materialsare alkyl aryl sulfonates, alkyl sulfonates, primary and secondary alkylsulfonates, products of oxyethylation of fatty acids, alcohols, alkylphenols, fatty amines, alkyl nephtols and mercaptans, quaternaryammonium compounds. The proportion of the surface-active material shallbe within 0.05-0.2 percent by weight of the moulding sand.

Any ground refractory material commonly employed in foundry work for theproduction of moulds and cores, such as quartz sand, olivine,chromo-magnesite, grog or chamotte, etc. can be used as a moulding sand.

What is claimed is:

1. A process of making foundry molds and cores from a fluidself-hardening sand or sand mixture with controllable propertiescomprising the steps of preparing (l) a mixture consisting essentiallyof parts by weight of molding sand, from 8 to 15 parts by weight ofhydraulic cement as a binder, (2) a mixture of from 0.25 to 1.5 parts byweight of an alkali-metal aluminate and from 0.5 to 2.0 parts by weightof an alkali-metal carbonate as the hardening accelerator, from 0.05 to0.2 parts by weight of a surface-active material with a foaming action;and water; mixing (1 and (2) to form a fluid mass; forming the foundrymold and cores from said mass and hardening said molds and cores in air.

2. The process as claimed in claim 1, in which the alkali-metalaluminate is sodium aluminate.

3. The process as claimed in claim 1 in which the alkali-metal carbonateis potassium carbonate.

4. The process as claimed in claim 1 in which the surface-activematerial is sodium alkyl aryl sulfonate.

5. In a liquid self-hardening mold or core mixture consistingessentially of 100 parts by weight of molding sand, from 8 to 15 partsby weight of hydraulic cement as a binder and from 0.05 to 0.2 part byweight ofa surface-active substance with a foaming action and aselfhardening accelerating additive, the improvement consisting of, assaid additive 0.5 to 2.0 parts by weight of potassium carbonate and from0.25 to 1.5 parts by weight of sodium aluminate.

6. The liquid self-hardening mold or core mixture as claimed in claim 5,wherein sodium alkyl aryl sulfonatc is the self-active substance with afoaming action.

1. A PROCESS OF MAKING FOUNDRY MOLDS AND CORES FROM A FLUIDSELF-HARDENING SAND OR SAND MIXTURE WITH CONTROLLABLE PROPERTIESCOMPRISING THE STEPS OF PREPARING (1) A MIXTURE CONSISTING ESSENTIALLYOF 100 PARTS BY WEIGHT OF MOLDING SAND, FROM 8 TO 15 PARTS BY WEIGHT OFHYDRAULIC CEMENT AS A BINDER, (2) A MIXTURE OF FROM 0.25 TO 1.5 PARTS BYWEIGHT OF AN ALKALIMETAL ALUMINATE AND FROM 0.5 TO 2.0 PARTS BY WEIGHTOF AN ALKALI-METAL CARBONATE AS THE HARDENNING ACCELERATOR, FROM 0.05 TO0.2 PARTS BY WEIGHT OF A SURFACE-ACTIVE MATERIAL WITH A FOAMING ACTION;AND WATER; MIXING (1) AND (2) TO FORM A FLUID MASS; FORMING THE FOUNDRYMOLD AND CORES FROM SAID MASS AND HARDENING SAID MOLDS AND CORES IN AIR.2. The process as claimed in claim 1, in which the alkali-metalaluminate is sodium aluminate.
 3. The process as claimed in claim 1 inwhich the alkali-metal carbonate is potassium carbonate.
 4. The processas claimed in claim 1 in which the surface-active material is sodiumalkyl aryl sulfonate.
 5. In a liquid self-hardening mold or core mixtureconsisting essentially of 100 parts by weight of molding sand, from 8 to15 parts by weight of hydraulic cement as a binder and from 0.05 to 0.2part by weight of a surface-active substance with a foaming action and aself-hardening accelerating additive, the improvement consisting of, assaid additive 0.5 to 2.0 parts by weight of potassium carbonate and from0.25 to 1.5 parts by weight of sodium aluminate.
 6. The liquidself-hardening mold or core mixture as claimed in claim 5, whereinsodium alkyl aryl sulfonate is the self-active substance with a foamingaction.